Q: Lost I phone

Hi, I lost my I phone 5 about 3 months back. Unfortunately i hadn't put any lock code in it. But I put it in to the lost mode. and I changed the apple ID password and my email password as well. But today I found out that someone has purchased a app using my account. Also amount from my credit card has been deducted. How would this be possible? Please advise me what to do next? I removed the phone in I cloud today.